電磁連鑄對Incoloy800H合金鑄坯內TiN分布和內裂紋的影響

電磁連鑄對Incoloy800H合金鑄坯內TiN分布和內裂紋的影響Effect of Electromagnetic Continuous Casting on TiN Distribution and Internal Crack of Incoloy800H Alloy Billet

研究開發了Incoloy800H耐腐蝕合金立式電磁連鑄制備方法,成功制備出截面為100 mm×100 mm的Incoloy800H連鑄坯,并研究了其內部凝固組織、內部裂紋和TiN分布等物理現象。結果表明,常規立式連鑄Incoloy800H鑄坯的內部組織粗大、存在嚴重的內部裂紋和大量TiN夾雜物;采用立式電磁連鑄后,制備的Incoloy800H合金連鑄坯的中心等軸晶率從2.45%增加至41.45%,且中心等軸晶的平均晶粒尺寸由10.83 mm 減小至1.28 mm,并有效地消除了內部裂紋。TiN數量與分布的研究結果表明,立式電磁連鑄條件下,鑄坯中心的大尺寸TiN (大于2 μm)數量由3.71×10-4 μm-2降至1.59×10-4 μm-2,使易于誘發內裂紋的TiN數量顯著減少,并抑制了TiN團簇的形成,有助于枝晶間的液態合金的補縮;另一方面,電磁連鑄促使Incoloy800H合金連鑄坯形成細小的等軸晶,減輕了合金元素偏析并減少了大尺寸TiN的數量,從而減少了萌發裂紋的機率,有效地抑制了內部裂紋的形成。

Incoloy800H is a kind of corrosion-resistant Ni-Cr-Fe base alloy with wide application in industrial fields. Vertical continuous casting process was developed to replace conventional mould casting process to increase product rate and decrease energy consumption. However, seriously internal quality issues of the continuously cast Incoloy800H alloy have been revealed. In this work, the square billet of Incoloy800H alloy, whose cross-sectional size were 100 mm×100 mm, were successfully fabricated in vertical continuous casting process with and without electromagnetic field (EMF), and the solidification structure, TiN inclusion distribution and internal crack were investigated. The result showed, without EMF, the Incoloy800H alloy billet had some seriously internal quality issues like coarse column grains, internal cracks and large TiN inclusion. With EMF, The equiaxed grain ratio of Incoloy800H alloy billet increased from 2.45% to 41.45%, the equiaxed grain size decreased from 10.83 mm to 1.28 mm and internal cracks were eliminated. TiN is a kind of detrimental inclusion in Incoloy800H alloy billet, which can act as stress concentration sites to form cracking. Most of TiN inclusions were located at interdendritic area and formed into TiN cluster to block interdendritic feeding channel. The application of EMF reduced the number of TiN inclusion from 3.71×10-4 μm-2 to 1.59×10-4 μm-2 in the center of billet. Further analysis illustrated that the EMF can refine the equiaxed grain size, reduce the degree of element segregation and the number of large TiN inclusion, which can reduce the probability of the crack initiation and inhibit the formation of TiN cluster to enhance the interdendritic feeding, thereby remarkably reduce the internal crack in Incoloy800H alloy billet.

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